1. Field of the Invention
The present invention relates generally to a method and apparatus for mounting a heat sink on a heat producing electrical circuit component.
2. Description of the Related Art
Heat producing components such as field effect transistors often require heat sinks to carry away the thermal energy produced by the component. To increase the heat dissipation of the heat sink by positioning the heat sink in an air flow, typical mounting arrangements for these heat producing components include providing a finned heat sink that is elevated off a mounting surface or circuit board to which the combined heat sink/component is mounted, and the heat producing component itself is typically mounted on the elevated surface of the heat sink instead of directly on the mounting surface. For field effect power transistors, the transistor may instead be mounted in a vertical orientation on a circuit board with the heat sink mounted to one side of the transistor, thereby positioning the heat sink in an air flow. In another arrangement, the field effect transistor is mounted horizontally on the circuit board or mounting surface and a heat sink is mounted on the opposite surface of the field effect transistor to position the heat sink in the air flow or the heat sink is mounted on an opposite surface of the circuit board from the field effect transistor.
Each of these methods for mounting a heat sink to a heat producing component requires a separate mounting step for the mounting of the heat sink from the step mounting the component, each requires a separate affixing location for the heat sink and the component, and each results in a relatively high profile structure.
An objective of the present invention is to provide a heat sink for a surface mountable heat producing component which affixes the surface mountable component to the circuit board and the heat sink to the surface mountable component in a single step. Another objective is to provide a low profile heat sink. A further objective is to provide a heat sink having a small foot print occupying a minimum area on a mounting surface. Yet a further objective is the invention is to minimize space interference between the heat sink and other components to be mounted on the mounting surface. Still another objective of the invention is to provide a surface mountable heat sink.
The invention provides the advantage of eliminating the need for a separate mounting step of a heat sink while permitting low profile surface mounting of the heat producing component, all without requiring mounting holes through the circuit board. The present invention also provides a low profile heat sink, enabling more compact circuits to be produced with tighter clearances between adjacent circuit boards, for example. The present invention also eliminates the need for multiple affixing locations by requiring application of solder only to a single surface for mounting of the component to a circuit board and for mounting of the heat sink.
These and other objectives and advantages of the invention are provided by a heat sink having a mounting plate which extends between a mounting surface of the heat producing component and the circuit board on which the component is to be mounted. The mounting plate of the heat sink is provided with solder conducting openings which pass through the plate. A solder pad is formed on the circuit board or on the heat producing component and the mounting pad is positioned against the solder pad so that during a solder reflow process, the liquid solder flows through the solder conducting openings to solder the mounting plate of the heat sink to the circuit board and to solder the heat producing component to the mounting plate of the heat sink.
The mounting plate of the heat sink is thermally connected to a heat dissipating element. The heat dissipating element may be a traditional finned heat sink structure. However, various preferred embodiments of the invention provide heat dissipating elements which present a low profile. In particular, the heat dissipating element in each of the preferred embodiments extends substantially parallel to the circuit board on which the component is mounted, and so provide a low profile for the component and heat sink combination from the surface of the circuit board. Miniaturization of the circuit is thereby facilitated.
For purposes of the present invention, the term heat producing component relates to any component to be cooled, and references to circuit boards or mounting locations refer to any location or surface at which the component is to be mounted.